The field of this invention is that of thermally responsive electrical switches and the invention relates more particularly to switches for performing electrical control functions on automotive engines in response to changes in engine temperature.
Controls for automotive engines have become increasingly more precise in attempting to improve fuel efficiency and reduce exhaust pollution emissions while maintaining suitable engine driveability and as a result there has been a growing need for low cost, thermally responsive controls which are rugged and reliable enough to perform control functions in an automobile environment in response to changes in engine temperature. Such controls are already being used in a wide variety of applications to provide temperature-indicating electrical signals to microprocessor-based engine control units and for regulating exhaust gas recirculation and distributor advance and the like through thermal valve regulation of vacuum lines. Such known controls also include controls providing direct regulation for individually operated electrical devices such as engine cooling fans and the like and more recently it has been found desirable to provide two speed regulation of engine cooling fans and/or regulation of two separate engine cooling fans so that, for example, one fan is operated under normal engine running conditions and the second is activated during overheating situations when the vehicle is standing in traffic or the like.
Many of such previously known thermally responsive automotive controls have been characterized by sturdy, low cost structures. Many have had a thermally and/or electrically conductive metal housing part secured to a molded housing part of an organic, electrically insulating material to form a chamber therebetween and such controls have incorporated one or more thermally responsive bimetallic members in the control chamber for providing desired control functions. However, the cost of making such control devices is very volume dependent and although control devices of the same general type find wide application it is frequently found that the devices require different operating conditions for serving various segments of the market. As a result, significant manufacturing costs are encountered in assembling devices to meet those individual temperature requirements. It has also been difficult to meet delivery schedules where determination of device operating temperatures are delayed or changed at the last moment.